Though it features few recognisable faces, this Australian-shot, US-set indie horror displays a core competency that gets it some of the way to where it’s heading – only to collapse in the final reels into the usual hacky manoeuvres. Ten years after fleeing a fundamentalist branch of the Latter-day Saints, snub-nosed artist heroine Elise (Elizabeth Cullen) has started shunning the attentions of boyfriend Adam (John Kim), instead obsessively digging holes in the couple’s back garden and trashing the living room in the middle of the night. Could it have something to do with the grimy cellar door she feels compelled to paint, or the traumatic baptism we witness in a pre-title sequence? What are the chances?

For somewhere between half and two-thirds of its running time, we’re watching a diagnostic case study: Elise and close pals return to Mormon country – more specifically, the in-no-way ironically named hamlet of Haventon – to undergo a regression therapy involving an ayahuasca variant; this will strike anyone as ill-advised even before an actual cellar door is uncovered outside and everybody starts throwing up. (Cue the especially dreadful line: “She must have torn internally.”) Thereafter, flashbacks reveal what’s been suppressed or concealed: the younger Elise’s growing closeness to the bishop’s daughter Clara (Luca Sardelis) would seem to indicate our girl isn’t possessed, merely bisexual.

The results prove middling at best, not on any level dealing the knockout blow that religious conversion practice deserves; nor is it ever the campy scream the set-up might have licensed. Cinematographer Michael Tessari gives matters a wintry, low-lit, persuasively un-Australian look, and gathers the odd suggestive image, like a dream sequence scattering of petals. More of that would have done Diabolic a world of good, but co-writer and director Daniel J Phillips heads the other way, cranking up the soundtrack’s parping and underlying Mormonphobia with supporting players going heavy on the repression and hysteria.